1. Technical Field
The present invention relates generally to safety fasteners for ballistic resistant helmets. More particularly, it encompasses fasteners designed to reduce the likelihood of secondary projectiles forming due to a nearby ballistic incursion.
2. Description of Prior Art
Ballistic helmets, primarily for military use, are capable of resisting ballistic threats through the design and manufacture of the helmet shell. One approach involves several layers of composite materials that are impregnated with resin and laminated together under pressure and heat. For example, layers of Kevlar® fabric may be impregnated with a thermoset resin that is molded to form the helmet shell. Steel helmet shells constitute another approach.
In order to adequately protect the wearer, helmets must remain strapped on through the use of various suspension, retention and chinstrap fitting equipment. Mounting of fitting equipment to the helmet shell requires bolting to bores formed in the helmet shell. The creation of these bores, and the external exposure of the bolt heads, compromises the ballistic safety of the helmet shell. In particular, instances of ballistic incursion in the vicinity of this mounting hardware presents an elevated threat, in the form of secondary projectiles. If the fastener fails, secondary projectiles may be created within the helmet shell or exterior to the helmet shell.
U.S. Pat. No. 6,854,921 discloses a ballistic resistant cap nut for use with a conventional screw bolt for securing the flight deck door frame on a commercial airliner. The cap nut achieves its ballistic resistance by employing titanium or stainless steel in an overdimensioned configuration to provide greater robustness. Such an approach would be unacceptable in a helmet environment due to the increased weight and excessive internal protrusion.
U.S. Pat. No. 5,600,084 discloses a conventional armor plate bolt fastener that captures a ballistic material web. The web is wrapped around the bolt head to secure a thin shield therein. The web and shield would be too heavy and provide too great an external protrusion for a helmet.
U.S. Patent Applications 2004/0058125 and 2005/0022658 utilize conventional screw and bolt fasteners to add layers of ballistic resistant panels to protect underlying structures. U.S. Patent Application 2003/0104738 discloses a multi-layered composite laminate, wherein various layers have different mechanical properties to improve shearout resistance along with better distribution of cutting and impact forces.
Accordingly, it would be desirable to provide a safety fastener that is lightweight, meets tighter standards for internal protrusion and minimizes the deleterious effects associated with forming mounting bores though the helmet shell.